1. Technical Field
The present invention generally relates to disposable filters for paint over spray collection or filters for fluid streams. More particularly, the present invention relates to a non-woven batting which is sliced to produce two filters simultaneously with three-dimensional waveform or zigzag patterns formed upon the fluid-receiving anterior filter surface.
2. Description of the Prior Art
In recent years federal and state governments have instituted laws pertaining to the paint industry and in particular to the chemical formulations of paints and minimum performance efficiencies of paint over spray collection devices. The essential driving force behind these laws is to decrease the emissions of volatile organic compounds and paint particulate into the atmosphere. To achieve these ends, the laws require a decrease in the solvent content permitted in paint formulations and establish efficiency criteria in the collection of particulate. The result is the improved quality of the atmosphere.
The resulting changes in paint formulations created new coating formulations, including, but not limited to, so-called “high solids” formulations and “water born” formulations. These newly developed coating formulations have thus presented filter manufacturers with a need to develop new filter constructions to more effectively filter the particulate from solvents during various paint processes, since the new coating formulations were difficult to collect in the previous types of filters for paint over spray and fluid particulate collection. Hence many innovations have been designed and introduced to improve the performance criteria of paint over spray and fluid particulate filters.
Performance of any paint over spray collection or fluid stream filter is measured by four criteria: efficiency, holding capacity, run off, and resistance. Efficiency is the ability of the filter to capture and retain paint and other fluid particulate from the air stream. It is defined as a percentage of the total particulate introduced to the filter; the higher the removal efficiency, the more effective the filter. Less paint or fluid particulate is emitted in the atmosphere. Holding capacity is defined as the amount of paint, defined by weight that the filter retains during its service life. The higher the holding capacity, the less paint runs onto the floor of the booth and the longer the service life of the filter. Less paint on the floor decreases clean up down time of the booth. Longer service life decreases filter change frequency and reordering. Run off is the amount of paint or fluid the filter knocks out of the air stream but does not hold. The paint or fluid runs off the filter onto the floor of the booth. Run off is defined by weight; the less run off, the less clean up expenses and production downtime in the paint booth.
Resistance measures the ease of the air passing through the filter. Resistance is the vacuum differential at the air leaving side of the filter. The initial resistance, initial pressure drop or IPD, is the measurement of a clean filter. The final resistance, final pressure of FTP, is the measurement of a paint-ladened filter at the end of its service life. The measurement is defined as a vacuum pulling a column of water up an incline tube. As a side to understanding, it is similar to the relationship between temperature and mercury rising in a glass thermometer. The higher the resistance, the more power is required to drive fans and motors which pull the air through the filters.
The resistance is critical to the proper design and operation of paint booths. Resistance controls fan size, horsepower, air movement requirements and booth balance. Lower resistance also increases the service life of the filters because the final resistance is set as criteria of the paint booth design. Therefore, if you begin at a lower pressure drop, it takes longer in time to reach the final pressure drop. All new art innovations in paint over spray and fluid filters are designed to improve some or all of the four criteria mentioned above. However, certain difficulties arise and a balance or compromise has to be found in the improvements.
Increasing removal efficiency is typically achieved by adding density through a tighter weave, smaller fiber, or more plies in the filter. Though an improvement in efficiency maybe achieved, historically this will decrease holding capacity and increase paint run off and resistance. The balance can be realized if face area, square feet, could be added to the filter. This would allow an increase in efficiency through densification of fiber and not adversely affect other performance criteria. Some of the more pertinent prior art relating to fluid filters and the like addressing the foregoing filter aspects are briefly described hereinafter.
U.S. Pat. No. 4,019,987 ('987 patent), which issued to Krasnow, discloses Extended Area Filters. The '987 patent teaches an extended-area filter for filtering plastic stock at high pressures has a breaker plate with an undulating surface confronting the oncoming stock which substantially doubles the available filter area. Screen packs having fixed therein the same surface configuration are supported uniformly on the undulating surface against collapse under the operating pressure.
U.S. Pat. No. 4,904,288 ('288 patent), which issued to d'Augereau, discloses a Filter Element for Circulating Air Systems. The '288 patent teaches a reusable air filter assembly for use in forced air heating and cooling systems includes an inlet stage filter medium consisting of a single layer of fabric woven in an egg-crate pattern and of relatively coarse polypropylene yarn, an outlet stage filter medium consisting of two layers of fabric woven in an egg-crate pattern of relatively fine polypropylene yarn and a precipitation chamber between said inlet stage and said outlet stage defined by a corrugated aluminum wire screen, with the precipitation chamber having a thickness, in the direction of air flow through the assembly, which is at least equal to the combined thickness of the inlet stage filter medium and the outlet stage filter medium. The filter assembly is supported in a corrosion resistant frame by opposing grid covers of expanded metal having a low friction coating thereon.
U.S. Pat. No. 5,034,042 ('042 patent), which issued to Allen, Jr., discloses a Structure and Filter for Paint Spray Booth. The '042 patent teaches a structure and a filter suitable for a paint spray booth, oven, or a combination booth and oven is described and includes outer walls enclosing the structure, only a portion of which provides the structural support for the booth's walls and roof. The interior of the booth has a plurality of filters on the walls and ceilings for supplying air from essentially the walls and ceiling to provide a more uniform air flow so that the painter is less exposed to vaporizing solvents, and when used as an oven, the heating is more uniform. Each of the filters made of a cloth material held in place by filter frames and may be used with either battens fixed to the frames or removable and held in place in pockets provided in the filter cloth.
U.S. Pat. No. 5,114,448 ('448 patent), which issued to Bartilson, discloses a high reliability, non-blocking air filter for filtering large volumes of low pressure air from equipment to be maintained free of dust and impurities while being ventilated during operation is disclosed. The filter media is mounted in a frame having a U-shaped cross section construction, which is attached over an air intake opening of the piece of equipment. The filter media includes a planar base surface and a plurality of projections. The tops of the projections define a surface above said planar base surface for supporting free-flowing articles so as such that these articles do not obstruct the air flow through the air intake filter.
U.S. Pat. No. 5,643,507 ('507 patent) and U.S. Pat. No. 5,648,641 ('641 patent), which issued to Berrigan et al., describe Filter Media having an Undulated Surface. The disclosed filter media comprise a web of melt blown microfibers having one surface substantially flat and the other surface having periodic wrinkle-like undulations. A method of making the filter media is also provided. The filter media is useful in electret filters when charged.
U.S. Pat. No. 6,071,419 ('419 patent), which issued to Beier et al., discloses a Fluid Filter, Method of Making and Using Thereof. The '419 patent teaches a fluid filter of a type akin to Paint Pocket type filter and includes a first batting of high loft, non-woven, fibrous fluid-permeable material with a plurality of openings formed through the thickness thereof across the length and width of the batting. A second layer of high loft, non-woven, fluid-permeable fibrous batting is attached to the first layer and extends across the entire length and width of the first layer. Preferably, the first and second layers are adhered together to form a single integral fluid filter. In the preferred form of the invention, the openings in the first batting have side walls which are perpendicular to the upper surface of the batting, such that fluid flow impacts on the upper surface of the batting, rather than directly impacting on the side walls.
U.S. Pat. No. 6,159,258 ('258 patent), which issued to Ager et al., describes a air filter elements with primary filter medias have foam pre-cleaners with an increased surface area provided by an upstream face which has peaks and valleys. In one embodiment, the peaks and valleys are defined by parallel ribs. If the filter element is a panel-type filter element having a pleated primary filter media, then, in accordance with one embodiment, the pre-cleaner is secured to the primary filter media by adhesive deposits on the peaks of the primary filter media. If the filter element is annular, the pre-cleaner is also annular and is slid axially over a perforated sleeve or screen on the primary filter media and held thereon by friction. By having the upstream surface of the foam pre-cleaner configured in peaks and valleys, the surface area of the upstream surface is increased substantially, which improves the capacity, efficiency and life of the filter element.
U.S. Pat. No. 6,602,328 ('328 patent), which issued to Doi et al., describes a gas turbine suction air filter which is provided wherein, despite a large capacity, dust is easily removed by an ultrasonic washer. A gas turbine suction air filter (1) has a box-like frame member (3) and a filter cloth (5) contained in the frame member (3). The frame member (3) is made of a metal material, preferably a stainless steel. The filter cloth (5) is formed having many pleats so that many folded faces (7) are formed. No intervening member is provided between adjacent folded faces (7, 7), with only a space being arranged there. The filter cloth (5) is a non-woven fabric of a synthetic resin fiber, preferably a polypropylene fiber. While this filter (1) has a large capacity, an ultrasonic wave reaches the entire filter cloth (5) when the filter (1) is washed by an ultrasonic washer.
U.S. Pat. No. 6,923,911 ('911 patent) which also issued to Beier et al., discloses a Method of Filtering Air Through an Air Passageway. The '911 patent describes a filter system for filtering particulate material from a generally unidirectional fluid stream comprising a first filter removably positioned in the fluid stream and a second filter removably positioned in the fluid stream downstream of the first filter. The first filter comprises a pre-filter and includes a layer of fluid-permeable material having a plurality of spaced-apart openings extending completely therethrough. The method of utilizing the fluid filter system of this invention is also disclosed and comprises the steps of: (1) removably positioning a first filter in the fluid stream; and (2) removably positioning a fluid-permeable second filter in the fluid stream downstream of the first filter. The first filter may be removed from the fluid when it becomes restrictive to air flow. The system may be operated so that the air may be passed through the second filter until the second filter becomes clogged or restrictive to air flow. The filters may be positioned in an air discharge passageway associated with a paint spray booth or may be positioned in an air intake passageway extending into a heating system, a ventilating system or an air conditioning system.
United States Patent Application No. 2002/0083692, which is authored by Richerson et al., teaches a filter apparatus for removing air entrained particles comprising a pleated filter media. A first media member has a plurality of alternating upstream and downstream folds and a wall connecting the folds. A pair of slits forms an aperture and a hinged pleat. A second media member matingly attaches to the first media member. United States Patent Application No. 2004/0088958, which is also authored by Richerson et al., teaches a filter apparatus for removing air entrained particles comprising a pleated filter media. A first media member has a plurality of alternating upstream and downstream folds and a wall connecting the folds. A pair of slits forms an aperture and a hinged pleat. A second media member matingly attaches to the first media member.
United States Patent Application No. 2006/0000196, which was authored by Beier et al., teaches a fluid filter which comprises a layer of high loft, non-woven, fibrous, fluid-permeable material having a length and a width, an upper surface, a lower surface, and a non-constant thickness measured between the upper and lower surfaces. The non-constant thickness is achieved by providing a series of spaced-apart grooves separated by a series of spaced-apart ridges. The lower surface is substantially planar and the grooves each have a generally U-shaped cross section with the ridges having a generally inverted U-shaped cross section. A modified form of the invention is also disclosed wherein the zones of higher flow resistance have a greater density than the zones of lower flow resistance. In this embodiment, the thickness of the filter is constant. The method of filtering particulate material from a fluid stream is also disclosed.
Of the various prior art filter constructions, perhaps two of the most effective are taught by Beier et al. in the '419 patent and the '805 patent. State of the art filter technology in the paint over spray and fluid filter industry include filters constructed from fiberglass, paper, polyester, and combinations of the above. The material advantages and disadvantages of incorporating these types of filtering media into a filter construction are well presented in the '419 and '805 patents. The noted patents further specify that filters for use in the paint overspray industries regularly have an overall length by width dimension of 20×20 inches. If the fluid-engaging surface were substantially planar, these dimensions would yield a maximum fluid-receiving surface area of roughly 2.78 square feet or 400 square inches. Notably, however, the '419 and '805 patents do not teach a fluid-engaging surface that is substantially planar or uniform.
The art represented by '419 and '805 patents essentially comprise two distinct layers of polyester batting fastened together in plies. The first or anterior layer comprises roughly teardrop, diamond, or ellipsoidally shaped apertures having a substantially uniform depth while the second or posterior layer is of uniform construction without apertures. The first or anterior later thus forms so-called “paint pockets” upon the second or posterior layer. The second ply or air-leaving ply is of a finer denure fiber weave for enhancing the filtering effect of the filter. A primary shortcoming with this construction is that at its very beginning of operation or service life, the paint laden air entering the filter bypasses the first or anterior layer and enters the filter by way of the paint pocket apertures, since filtered fluid streams follow the path of least resistance through the filtering plane(s) and the apertured regions represent pockets of decreased flow resistance. This mechanism negates many of the filtering benefits that the apertured layer may have otherwise contributed to the filtering effect of the filter.
Bearing in mind that the Beier et al. paint pockets may be roughly modeled as ellipsoidally shaped apertures, and taking a 20 inch by 20 inch filter as an exemplary filtering plane, the Beier et al. filter comprises roughly 110 paint pockets in any given 20×20 filter. Each paint pocket comprises a major axis of about 2 inches and a minor axis of about 1 inch. The area of an ellipse is given by the relation: Aellipse=πa b, where “a” is the semimajor axis (a=1 inch=one half the length of the major axis) and “b” is the semiminor axis (b=½ inch=on half the length of the minor axis). The transverse fluid-receiving area of a single paint pocket is thus roughly 1.6 square inches. If this figure is multiplied by the number of paint pockets (110) in a given filter, the effective initial fluid-collection surface area is roughly 175 square inches paint pocket is thus on the order of less than or about half the total available filtering surface area.
Notably, there is only one layer of media at the bottom of the paint pocket, and thus there is less initial resistance to fluid flow because the fluid or air is essentially passing through only one layer of media. Therefore, the air flow through the paint pocket initially experiences a higher air flow rate and thus collects more paint or fluid particulate until the resistance to fluid flow at the paint pocket equals the resistance of the area represented by the two ply sections of the filters. Other avenues of decreased air flow resistance include the side walls of the paint pockets. For the air flow to pass through the side walls of the paint pocket it must deviate from a straight line path up to 90 degrees. However, as the name implies, particulate and solvent (paint overflow) is all the while collecting in the paint pocket and air flow continually and dynamically decreases. Beier et al. have attempted to remedy pocket collection of fluid-borne particulate as set forth by the construction disclosed in United States Patent Application Publication No. 2006/0000196. It may be seen from an inspection of the noted publication that Beier et al. have attempted to round the upper fluid-receiving or fluid-contacting surfaces so that air flows drawn into the filter would not meet planar air-to-filter interfacing and for increasing the filtering surface area of the filter. Further, the anterior filter surface was sinusoidally contoured in one dimension for creating substantially linear channels for directly allowing paint run-off when installed such that the channels are longitudinal or vertical. This design, however, provides only a modest increase in filtering surface area and unimpeded paint run off poses a significant problem since the media should function to filter and hold paint overflows.
Given that hundreds of thousands of pounds of paint may be annually dispensed in any given painting operation, filter particulate removal efficiencies are critical for minimizing solvent effluent and other associated costs. By way of example, a filter quoted as providing a removal efficiency of 99.84% versus an actual tested removal efficiency of 99.71% yields an efficiency difference of 0.13%. If the painting operation is expecting to remove 99.84 percent of 500,000 pounds over overspray, while only removing 99.71 percent of 500,000 pounds of overspray is actually filtered, then roughly 650 pounds of overspray may go unreported and is unknowingly lost to the environment. Thus, it should be clear from the foregoing that enhancements in filter design are of critical importance to the industry and the environment.